1. Field of the Invention
This invention pertains to fibrous substrata for soil-free or hydroponic cultivation.
2. Discussion of the Prior Art
The constantly developing practice of soil-free cultivation has led to the utilization of substrata of various natures, especially vegetable-derived fibrous materials, natural mineral products such as gravels and pozzolanas, or else processed mineral products such as expanded perlites or rock wools.
The choice of substratum depends at once on its characteristics which facilitate cultivation, good solution retention, good aeration, geometric and chemical stability, etc . . . , and economic data such as: cost of the substratum, replacement frequency, as well as the necessary investment, depending on the type of cultivation under consideration, which, can be related to the type of substratum utilized.
Among the processed mineral materials, rock wools present advantageous properties. They offer a very high degree of porosity, of about 95%, good water retention and good aeration. The material is also easy to handle due to its lightness. On the other hand, the cost of these substrata normally leads to multiple uses, for obvious economic reasons. These uses require disinfection, thus handling, which becomes increasingly difficult after successive cultivations because the structure of the material deteriorates. The deterioration of the material also causes a loss of porosity and sinking, which change the cultivation conditions.
Among the advantageous characteristics of the rock wool substrata, the "available" quantity of water retained presents a particular interest.
This characteristic determines the safety margin which is available to maintain the satisfactory moisture conditions. The greater this available water value is for a given volume of material, the greater the degree of safety. If the material presents a large quantity of available water, the feed of liquid to the substratum during cultivation can be effected at less frequent intervals. Still better, the volume of substratum which is necessary for cultivation can be decreased when the available water quantity per unit of volume increases.
The latter characteristic is of great practical interest. A smaller volume of substratum, and more precisely, a smaller amount of fibrous materials, leads to a less costly material. When this decrease in cost is sufficient, it can be accompanied by other advantages, in particular, below a certain threshold, the one-time use of substratum can be envisioned, which allows the elimination of the operations required for the sterilization of the substratum between successive cultivations.